Technique

Photography

Light, and light-sensitive (photosensitive) material, are the key elements of photography. The word is made up of the Greek genitive noun photos, ‘of light’, and the verb graphein, ‘drawing’. Hence, ‘drawing of/with light’. Using light and other forms of radiation, images are captured on photosensitive material. Analogue photography stores the image information, which has passed through the lens as light, on a light-sensitive film. This film then has to be treated chemically (developing the negative) to allow the subsequent printing of the photographs, which requires another chemical process.

Digital photography has obviated the need for light-sensitive film. Instead, a light-sensitive chip (CCD), governed by the electronics and software on the camera, stores the image information in the camera’s memory. The image obtained can be manipulated on computer using a range of software and can be printed. There are many techniques for printing analogue and digital photographs, including C-printing and gelatin silver printing, to name but a couple. These prints can also be glued to plates of materials such as aluminium or sandwich panel (aluminium composite / dibond).

C-print, short for chromogenous colour printing, is perhaps the commonest printing technique in photography. What characterises the colour photography techniques known as chromogenous is that there is a reaction between two chemicals that give rise to colours, which form the photographic image. Chromogenous images are composed of three distinct layers of primary subtractive colours — magenta, cyan and yellow (the complements of red, blue and green) — which in combination will make up a full-colour photographic image. In each of these layers, there is a light-sensitive material, composed of silver halide emulsion. A C-print can be produced from a colour negative, a slide or a digital image. Where a digital image is used, the C-print will be printed using a Lambda machine (produced by Durst) or a LightJet (by Océ). Accordingly, one often hears prints of digital photographs referred to as Lambda prints or LightJet prints.

Silver prints (which may be gelatin silver prints) are a generic name for all types of photographic prints made using paper coated in a photosensitive salt of silver, such as silver bromide or silver chloride. Gelatin silver prints are made up of four layers: a paper base, baryta paper, gelatin binder, and a protective gelatin topcoat. When this assemblage is exposed to light, the silver particles in the salts react to it and form the latent image. The film can then be developed in a chemical bath that strips away the silver halides around that latent image. With gelatin silver prints, the image is not locked into the fibres of the photographic paper, but hangs, as it were, above the surface. Gelatin silver prints are susceptible to oxidation of their materials, which will cause yellowing and loss of sharpness of the image. Gelatin silver prints emerged around 1880 and remain a leading technique for printing monochrome photographs.